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It’s possible that Justin Smith is the best defensive lineman in the history of the NFL. Or Superman. Or, at the least, Batman.

2013 49ers Fan Photos

Sometimes, that’s the way it seems as the 49ers head into a matchup against the Seahawks in Seattle Sunday night.

With Smith out of the lineup last December with a triceps injury suffered the week before, the 49ers were mauled by the Seahawks 42-13.

After having beaten Seattle in three straight meetings – all with Smith starting at right end in their 3-4 alignment – the 49ers fell quickly behind, 21-0 in their December clash and gave up 346 total yards to Seattle.

Now, with the teams getting ready for their first meeting since that game, NFL observers and the 49ers themselves say Smith’s return will make this game much different.

“With Justin Smith out with a torn triceps, (linebacker) Aldon Smith pretty much became a non-factor,” wrote NFL analyst Elliot Harrison, in his preview for Sunday night’s game. “Things can’t go that way in Seattle this time.”

Watch Justin Smith over the course of any game, and you see a defender who must be accounted for on every play. He is relentless, against both the run and pass, and his strength and technique allow him to disrupt plays and let the 49ers’ terrific linebackers make the tackle on running backs or loop into the backfield on stunts for sacks.

When No. 94 was out for the final games of the regular season in 2012 – and then not up to full strength in the postseason – the Niners defense just wasn’t as strong as it had been. The team was vulnerable against the run and its pass rush disappeared.

“It was a big factor,” 49ers inside linebacker Patrick Willis told the Bay Area News Group, of Smith’s absence in last year’s loss at Seattle. “Justin, to me, is one of the best defensive players in the league. Anytime he’s not out there, we miss him. But we’ve got him back now. We know he’s going to be a difference-maker, as always.”

This season, the 49ers' goal is to keep Smith fresher for the long haul. By adding some depth to the defensive line over the offseason, Smith can get a rest now and then. In the opener against the Packers last week, Smith played 52 of 62 snaps. Smith was in on only three tackles against Green Bay, but his presence allowed linebackers to make 19 tackles, hold the Packers to 63 yards rushing and sack Aaron Rodgers twice.

This week, 49ers defensive coordinator Vic Fangio said that Smith’s presence helps San Francisco across the board.

“Justin is a complete player,” Fangio told Cam Inman of the Bay Area News Group. “He’s not one-dimensional. He helps us both defend the run and the pass.”

Seattle offensive coordinator Darrell Bevell agrees, telling the media this week that Smith frees up other players to make plays and makes a huge difference when he’s on the field.

“He’s very savvy with his technique,” said Bevell. “He gets great push.”

But Sunday night marks a clash between perhaps the two best teams in the NFC. It’s a matchup between two of the NFL’s best young quarterbacks (Colin Kaepernick and Russell Wilson), best defenses, best coaches (Jim Harbaugh and Pete Carroll) and best running games (led by backs Frank Gore and Marshawn Lynch). Each team has been picked by various analysts to go to the Super Bowl. The 49ers have won two straight NFC West titles, but the Seahawks want to prove they’re the big dogs in the division, and they’ll have the very loud home-field advantage at CenturyLink Field, where the noise level last December seemed to rattle the 49ers once they fell behind.

Oddsmakers have made Seattle a 3-point favorite, and since Wilson won the Seahawks quarterback job, his team has never lost at CenturyLink.

So, Sunday night’s game isn’t about just one defensive lineman for the 49ers. But to his teammates, Justin Smith is a difference-maker, and could be the key to beating Seattle on its own turf.